Multi-half-tone imaging and dual modulation projection/dual modulation laser projection

ABSTRACT

Smaller halftone tiles are implemented on a first modulator of a dual modulation projection system. This techniques uses multiple halftones per frame in the pre-modulator synchronized with a modified bit sequence in the primary modulator to effectively increase the number of levels provided by a given tile size in the halftone modulator. It addresses the issue of reduced contrast ratio at low light levels for small tile sizes and allows the use of smaller PSFs which reduce halo artifacts in the projected image and may be utilized in 3D projecting and viewing.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims the benefit of priority toU.S. patent application Ser. No. 17/107,700 filed on Nov. 30, 2020,which is a continuation and claims the benefit of priority to U.S.patent application Ser. No. 16/366,618 filed on Mar. 27, 2019, now U.S.Pat. No. 10,855,960 issued Dec. 1, 2020, which is a continuation andclaims the benefit of priority to U.S. patent application Ser. No.14/890,133 filed on Nov. 9, 2015, now U.S. Pat. No. 10,257,477 issuedApr. 9, 2019, which is a 371 of International Patent Application No.PCT/US2014/034010 filed Apr. 14, 2014, which claims the benefit ofpriority to U.S. Provisional Patent Application No. 61/820,680 filed May7, 2013; and U.S. Provisional Patent Application No. 61/820,683 filedMay 7, 2013, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to display devices and more particularlyto dual modulation projectors (including laser projectors) and thecreation of half-tone images in a pre-modulator of the projector.

Discussion of Background

Dual modulation projectors and displays include display devices (e.g.,Whitehead U.S. Pat. No. 7,403,332, and Daly U.S. Pat. No. 7,064,740) andprojectors (e.g., Sayag U.S. Pat. No. 7,002,533).

SUMMARY OF THE INVENTION

The present inventors have realized the need for improved half-toning ofpre-modulator images. The invention allows the use of smaller halftonetiles on the first modulator of a dual modulation projection system.This techniques uses multiple halftones per frame in the pre-modulatorsynchronized with a modified bit sequence in the primary modulator toeffectively increase the number of levels provided by a given tile sizein the halftone modulator. It addresses the issue of reduced contrastratio at low light levels for small tile sizes and allows the use ofsmaller PSFs which reduce halo artifacts in the projected image. Thehalf toning may also be utilized to improve projection of color orpolarization separated 3D imagery.

Portions of both the device and method may be conveniently implementedin programming on a general purpose computer, or networked computers,and the results may be displayed on an output device connected to any ofthe general purpose, networked computers, or transmitted to a remotedevice for output or display. In addition, any components of the presentinvention represented in a computer program, data sequences, and/orcontrol signals may be embodied as an electronic signal broadcast (ortransmitted) at any frequency in any medium including, but not limitedto, wireless broadcasts, and transmissions over copper wire(s), fiberoptic cable(s), and co-ax cable(s), etc.

The present inventors have realized the need to increase contrast andbrightness of projection displays and to reduce artifacts. The presentinvention includes generation of a digital PSF. The digital PSF may be,for example, a digital PSF of a modulated light source to illuminate amodulator of a projector or other display. The illuminated modulator maybe, for example, a primary (or final) modulator of a dual modulationprojection system, an intermediary modulator of a multimodulationsystem, or, alternatively, any other modulator within a projection ordisplay system.

The digital PSF provides, for example, a PSF of any of a pixel, tile, orother area of a pre-modulator image or other lighting illuminating theprimary (or other) modulator that is configurable to account forvariations, discontinuities, aberrations, or other non-uniformities in alight path between the pre-modulator and primary modulator such that auniform PSF is exhibited at the primary modulator. The digital PSF maybe utilized to assure a consistent PSF among all pixels (or any group ofpixels) in an image, image path, or as illuminated on the primarymodulator.

In one embodiment, the present invention provides a dual modulationprojector containing a pre modulator, relay optics, and a primarymodulator, and where pre-compensation for imperfections of the relayoptics PSF is made by modifying the image sent to the pre modulator(pre-modulator image). The result is a desired uniformity and/or shapeof the light illuminating the primary modulator.

The desired uniformity and/or shape of the light illuminating theprimary modulator may be different for different portions of the image.The pre-compensation may be a filter that is different for differentregions of the image. The resulting PSF of pixels of the lightilluminating the primary modulator may be flatter in areas of the imagehaving predominately lower spatial frequencies, and the resulting PSF ofpixels of the light illuminating the primary modulator may be sharper inareas of the image having predominately higher spatial frequencies. ThePSFs may be different based on wavelengths of light being modulated. Inone embodiment, all PSFs in a region of the image have similarly shapedPSFs when illuminating a corresponding area of the primary modulator.The shapes of the same lights may be different before transfer optics orother optical elements in the light path between modulators, thedifferences being pre-compensation that adjusts the light to account forhow the different lights change enroute to the primary modulator.Ideally, the compensation is different for each wavelength of lightwhich reacts differently to different optical elements within the lightpath.

The pre-compensation filter may include coefficients are calculatedbased upon PSF measurements and a reference desired PSF.

Additional compensation is made by the primary modulator. The additionalcompensation includes, for example, compensation to further modulate thelight illuminating the primary modulator into the desired image. Theadditional compensation may also include compensation for a PSF of oneor more pixels.

The pre-modulator may be, for example, a DMD “displaying” a halftoneimage. The primary modulator may also be a DMD. The invention may beimplemented on combinations of reflective and transmissive modulatorswith any of polarizers, reflectors, dichroics, PB S s, or other opticalelements as relay optics between the modulators. The pre-modulatoritself may be illuminated by any combination of broadband light sources,narrowband light sources, modulated light sources. Preferably, thepre-modulator is illuminated by a laser light source that is at leastglobally dimmed and may include some form of local dimming (or spatialmodulation) to further increase contrast.

The invention includes a half-tone or other image on a pre-modulatorthat is changed multiple times per frame, and where bit sequences thatenergize the pre-modulator for each of those multiple times per frameare synchronized with corresponding energization signals of the primarymodulator. The invention includes a pre-modulator DMD energized with ahalftone image and a primary modulator DMD. The pre-modulator'shalf-tone image is changed multiple times per frame, and where the bitsequences on the pre-modulator DMD the primary modulator DMD aresynchronized, such that an average across the frame is the product of anaverage of the pre-modulator images through the relay optics and theprimary modulator image. In various embodiments, the pre-modulator halftone image is changed any of twice, three times, four times, and eighttimes or more per frame. The number of times per frame that thepre-modulator image may change may be variable, such that, for example,for some frames the pre-modulator image is changed twice per frame, andfor other frames it is changed 4 times per frame. The number ofpre-modulator half-tone changes may be updated when transitioningbetween 2D and 3D projection modes or transitioning between single anddual projector modes, or utilizing additional projectors. The number ofhalftone changes may be changed when transitioning between differentenvironments. The number of half tone changes may be different fordifferent projectors and/or similar projectors in differentenvironments, for example when displaying cinema content to riders in atheme park ride as they transition from scene to scene in differentportions of the ride that may utilize different projectors or aplurality of similar projectors in different environments.

The DMDs are synchronized such that the average across the frame is theproduct of the average of the pre-modulator images through the relayoptics and the primary modulator image.

In one embodiment, the pre-modulator half-tone image is changed three ormore times per frame and in synchronization with the final modulatorimage that is changed at least once per frame.

The present invention includes a method of energizing a pre-modulator,comprising the steps of:

-   -   1) Obtaining a 2D PSF of relay optics or other non-uniformities        in a light path between the pre-modulator and a primary        modulator;    -   2) Calculating a correction factor comprising difference between        a desired PSF and the 2D PSF;    -   3) Applying the correction factor to a pre-modulator image; and    -   4) Energizing the pre-modulator with the corrected pre-modulator        image.

The invention allows the use of less than optimal point spread (PSF)functions in the optics between the pre-modulator and primary modulatorof a dual modulation projection system. This technique uses multiplehalftones per frame in the premodulator synchronized with a modified bitsequence in the primary modulator to produce a compensation image thatreduces the errors produced by the sub-optimal PSF.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an illustration of the effects of the number of discretepre-modulation levels on local contrast;

FIG. 2 is an illustration of improved results obtained when the halftoneimage is distributed across 4 subframes;

FIG. 3 is an illustration of an example PSF and a corrected PSF; and

FIG. 4 is a diagram of an example bit sequence.

FIG. 5 is a schematic diagram of a dual modulation display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 shows schematic diagram of a dual modulation display. Display 10comprises a light source 12. Light source 12 may comprise may comprise,for example: a laser; a xenon lamp; an array of laser diodes or othersolid-state light emitters; an arc lamp; or the like. Alternatively,light source 12 may comprise at least 2 sets of light wavelengths eachset comprising red, green, and blue wavelength lights wherein at leastone of the same color wavelengths in different sets are separated by aminimum bandwidth necessary to accomplish off-axis viewing withoutcross-talk through passbands of viewing glasses at normal and off-axisviewing encountered in a standard cinema theater or cinema presentationat a theme park or as part of a theme park ride. The off-axis viewingmay be one of approximately 20 degrees and not more than 20 degrees, anda max angle normally encountered in the presentations.

Light 13 from light source 12 illuminates a first spatial lightmodulator 14. First spatial light modulator (“Pre-Modulator”) 14comprises a plurality of controllable elements 16. First spatial lightmodulator 14 may comprise a MEMS or a DMD in some embodiments. Secondspatial light modulator (“Primary Modulator”) 20 may comprises aplurality of controllable elements 22, accepting light 25 from thepre-modulator (through a set of relay optic elements 26). Controller 18sends control signals (e.g., energization signals) to both pre-modulatorand primary modulator, wherein the dual modulation energization signalsmay comprise a pre-modulator energization signal comprising more thanone half-tone image each to be displayed or energized on a pre-modulatorof a dual modulation display system during a single frame time period insynchronization with a primary modulator signal comprising an image tobe displayed or energized on a primary modulator of the dual modulationdisplay system. Further, the half-tone images may be generated via tileson the pre-modulator, wherein each tile comprises an array of modulatingelements—e.g., wherein each tile may comprise a n×n array of mirrors.

Light from the primary modulator may be transmitted through a projectorlens 28 and projected on screen 29. The image on screen 29 may be viewedby a viewer wearing active glasses 40 (e.g., configured for 3D viewing).User may be sitting in a theater and viewing the image on screen 29 atsome off-axis angle.

The current dual modulation POC EDR projector uses a single half toneimage per frame on the pre-modulator. To limit halo size on small brightfeatures and to achieve high local contrast, a small PSF is desirable.The first nonzero premod level is achieved by superimposing a field ofPSFs to achieve a relative flat light field. For a given (small) PSFsize, the spacing of the half-tone non-zero pixels must be smaller thanthe PSF, and small enough to achieve this flat field. This limits thepercentage of pixels that must be non-zero to a certain level, and thisdetermines the first nonzero average level, and the number of discretelinear pre-modulation levels. For example, a PSF that must be repeatedon a 5×5 grid will require 1 of 25 pre-modulator pixels to be turned on,resulting in a minimum 1/25 non-zero level, and 25 discrete premodlevels.

The image from the system described can have about 25× the contrastratio (CR) of the primary modulator; if the original CR of the primarymodulator was 1800, then the final image could have CRs of 45,000:1.This assumes that 1 of 25 pixels are always on. Since the premod DMD iscapable of >1800:1 CR, with the premod pixels off, the black level couldbe much better than 1/45000 of peak white; however turning off all ofthe premod pixels can have deleterious effects. These effects are alsopresent in the images at low light levels, even with some pixels on. Forexample, some image features vary with spatial frequencies beyond thosethat can be represented by the premod light field. For these imagefeatures, the premod light field will be constant, un-modulated. Thelevel of the premod light field will be determined by local max of theimage feature. The primary DMD must reduce the premod light field toproduce all levels of the local image feature. Depending on the firstnonzero premod level, the primary DMD might not have sufficient contrastto produce the lowest levels, limiting the local contrast of that imagefeature enough to affect its appearance. This is especially criticalaround the area where the last pixels on the premod tiles are turnedoff. In this area the local contrast goes down to around 20. Theseissues could be resolved by increasing the size of the PSF and tile, butthis would increase the halo size, which also can produce visibleartifacts.

FIG. 1 helps illustrate the issues. The blue line (starting on thehorizontal axis between 10E-6 and 10E-5) represents the best ContrastRatio that could be achieved in this particular auditorium with an idealinfinite contrast ratio 100 nit capable projector. This limit is causedbecause the room has a dark level of 0.0005 nits as measured at thescreen. This is from ambient room light in the room that reaches and isreflected from the screen to the viewer. The red line (starting on thehorizontal axis between 10E-4 and 10E-3) represents a single modulationprojector. The projector has an 1800:1 contrast ratio (simultaneous andsequential). As the peak level of the local image gets darker with thisprojector, the contrast ratio in the local image decreasesproportionally because the dark level is constant. This is normal andexpected behavior.

The light green line (the thinner line) represents the contrast ratiopossible with a dual modulation projector with high spatial frequencycomponents (where the premod is locally constant). As the projectedimage gets locally darker just out of peak white, the contrast ratiocurve matches exactly the previous case. However, when the level reaches(in this example) about 24/25 of peak white, the premod can change itsvalue from 25/25 to 24/25 pixels on, and the primary modulator can againuse its full range. Thus, for this lower light level we again have full1800:1 local contrast ratio. For the situation just before the premodchanged its value (to 23/25), the local contrast ratio would be reducedto 24/25*1800. This situation proceeds through each change in thepremod, with the possible CR resetting back up to 1800 after eachchange. For example when 2 pixels are active, the CR goes down to 144(2/25*1800). When only a single pixel is active, the premod cannotchange until the leakage light through the pre-modular is high enough toachieve the desired output level with the primary modulator alone (fullon). In the illustrative example, this level is 1/1800 of the outputpeak. There is a large gap between the lowest modulation level achievedby the half-ton at 1/25, and 1/1800, and in this zone the premod must bekept at the 1/25 level. The primary modulator is the sole modulator forthis region, and the contrast ratio falls to a level of about 1/25before the premod halftone can be set to zero. This level issignificantly lower (below the blue line by about a factor of 4) thanwhat could be obtained in this room with an ideal projector.

One purpose of this invention is to reduce the effects of theseartifacts by increasing the number of levels in the pre-modulator, butwithout increasing the tile size or PSF size. The concept is relativelysimple; use more than a single halftone image per frame. In the earlierdescription a 5×5 tile was examined. The following describes using a 5×5tile, but using 4 subframe halftones per frame. In this example, on anindividual pixel basis for each tile, the pixel can take on a sequenceof 5 values, these being 0, 1, 2, 3, or4 subframes (0, 1/4 frame, 1/2frame, 3/4 frame, or 1 frame). This allows the 5×5 tile to express 100positive values (and 0) rather than the original 25 values (and 0). If aDMD (TI Digital Mirror Device) is used for the primary modulator,modification of the bit sequences for the modulation chips will berequired. The DMD uses a form of pulse width modulation to modulate thelight; therefore, the light is required to be constant during the entireframe period. Changing the pre-mod halftones during the frame (4 times)would produce a non-constant light, and interfere with the PWM result.

Normally the DMD is used with a single sequence per frame to obtain a 16bit per pixel modulation. It is proposed to modify the bit sequence sothat the higher order bits are spread across the frame period;therefore, they are repeated multiple times. For example, if the top 14bits (of 16) are repeated, this would allow a pattern with the top 14bits repeated 4 times. The lower significant bits would remainunaffected, (spread across the entire frame period). This type ofrepeated sequencing has been described in the literature and is used toreduce motion artifacts with DMD based projection systems. U.S. Pat. No.5,986,640 describes a similar technique. The halftone image on thepre-modulator would be synchronized with the repeated sequences in theprimary modulator such that both modulators would change to a newsequence at the same time.

FIG. 2 illustrates the improved results obtained when the halftone imageis distributed across 4 subframes as described above.

For this situation, the lowest contrast ratio from the projector isapproximately equal to the results that could be obtained with an idealprojector in this room. This technique reduces the undesirable contrastratio reduction without increasing tile size and corresponding PSF size.

The current dual modulation POC EDR projector uses a single half toneimage per frame on the pre-modulator. A problem arises when the PSF ofthe relay optics between the two modulators is sub optimal, especiallywhen the resultant PSF is multi-lobed, or non-monotonic in anydirection. In order to compensate for sub-optimal PSFs with a singlehalftone image, the compensation is performed in the primary modulator.This can be done if the PSFs are reasonably well controlled across theframe and with the use of multiple PSFs within the dual modulationalgorithm, and interpolation between PSFs across the frame. Ultimately,one could use a different PSF for every pixel within the frame, but thiswould create additional computation burden. In addition, theregistration between the two modulators should be precise, and there aresome limitations due to the limited contrast ratio of the primarymodulator. Also, measurement or alignment errors may show up as highspatial frequency errors in the final image.

FIG. 3 shows a couple of examples of PSFs from the relay optics. Theleft PSF 310 is sub-optimal (with lobes 315), while the right PSF 320 isdesirable (with more regular contour 325).

It would be better if the apparent PSF at the primary modulator was wellcontrolled. One way of obtaining this is to average over several PSFs.As a practical matter, a single pixel turned on in the halftone image ofthe pre-modulator produces a small enough point to produce a pointspread function on the primary modulator; thus the PSF can be measuredon the projected image by turning the primary modulator to all white inthe presence of single ‘on’ pixels in the pre-modulator.

Normally, in a dual modulation system we are rarely if ever turning on asingle pixel in the pre-modulator, therefore multiple PSFs are typicallypresent. If the PSFs are significantly larger than the tile size (whichlimits the highest spatial frequency that can be obtained) of thehalftone image, one can obtain a PSF correction for the pre-modulatorimage which is used to generate the halftone image. The process may beimplemented as:

-   -   1. Obtain 2D PSF of relay optics and its 2D Fourier Transform.        rpsf(x,y), RPSF(wx,wy.    -   2. Specify desired PSF dpsf(x,y), DPSF(wx,wy.    -   3. Calculate the correction factor        Zc(x,y)(wx,wy)=DPSF(wx,wy)/RPSF(wx,wy) for a large number of        regions in the image, and interpolate to obtain a smoothly        changing Zc as a function of x,y. Obtain inverse Fourier        Transform of Zc(x,y)(wx,wy)=zc(x,y)(x,y).    -   4. Apply Zc to each region of the premod image. This might be        best done in the location domain as Corrected Image Cl=zc        convolved with the premod image.

These calculations determine a correction factor that filters thepremodulator image in such a way that when combined with the PSF of theoptics an image is produced where the inconsistencies of the optics PSFis smoothed to the desired psf. Of course, this only works if the relayoptics PSFs are larger than the smallest feature that can be obtainedfrom a halftone conversion of the premod image. This last point isimportant, as it limits the application of this approach to requiringlarge relay optics PSFs.

Addressing the halftone feature limitation requires an approach similarto that described above. In this implementation, instead of increasingthe number of levels for the halftone image, we could use the sametechnique to decrease the size of the halftone tiles, so that thefeature size was reduced.

As an example, let us assume that we originally had a 4×4 tile (16levels), and we now divide the picture frame into 4 sub-frames. The tilesize can now be reduced to 2×2 and still obtain 16 levels. The featureresolution in the halftone image has doubled, allowing smaller relayoptics PSFs to be compensated.

The amount of effort to compensate for the PSFs has not reduced from theoriginal design where all of the correction was done in the primarymodulator, however, this approach reduces the visibility of errorscaused by misalignment and measurement error verses the originalapproach using the primary modulator. These errors are translated intolow frequency type errors which have lower visibility.

As described above, if a DMD (TI Digital Mirror Device) is used for theprimary modulator, modification of the bit sequences for the modulationchips will be required. The DMD uses a form of pulse width modulation tomodulate the light; therefore, the light is required to be constantduring the entire frame period. Changing the pre-mod halftones duringthe frame (4 times) would produce a non-constant light, and interferewith the PWM result.

Normally the DMD is used with a single sequence per frame to obtain a 16bit per pixel modulation. It is proposed to modify the bit sequence sothat the higher order bits are spread across the frame period;therefore, they are repeated multiple times. For example, if the top 14bits (of 16) are repeated, this would allow a pattern with the top 14bits repeated 4 times. The lower significant bits would remainunaffected, (spread across the entire frame period). This type ofrepeated sequencing has been described in the literature and is used toreduce motion artifacts with DMD based projection systems. U.S. Pat. No.5,986,640 describes a similar technique. The halftone image on thepre-modulator would be synchronized with the repeated sequences in theprimary modulator such that both modulators would change to a newsequence at the same time.

A proposed sequence that could operate under the requirements of thepresent invention is illustrated in FIG. 4 .

The single sequence 410 illustrates a standard half-tome only modulatorsequence for a single frame 440. The double sequence 420 illustrates thesingle sequence divided into two partitions for the frame 445. The quadsequence 430 illustrates the single sequence divided into fourpartitions for the frame (e.g., 452, 445, 454). The divided sequencesare, for example, provided different bit sequences representingdifferent half-tone images applied to the same frame (and, for example,the same primary modulator image). The divided sequences may alternatebetween a first and second halftone image. The divided sequences mayimplement a rotating sequential application of first, second, and thirdhalf-tone images for each frame. The half-tone images implemented foreach frame include, for example, compensation of relay optics or othervariations as described above. Based on the above disclosure, many othersequences may be developed, customized, synchronized or chained togetherto perform the same result, any one or more of which may be implementedtogether or separately in conjunction with any other aspect (or aspects)of the present invention.

The pre-modulator is preferably illuminated by laser light sources andthe compensation of the pre-modulator image preferably compensates forwavelength specific aspects of the relay optics. Preferably, the resultis a PSF of each pixel (or groups of pixels) for each of the half-toneimages that are similarly shaped and varying smoothly from one-pixel tothe next. The shapes of the PSFs in groups of pixels in regions of theimage being modulated are the same or similar and any differencesbetween PSFs of neighboring regions may, preferably, smoothly transitionfrom the first region's preferred PSF to the adjoining region'spreferred PSF. For 3D projections, the premodulator image is compensatedto account for wavelength differences and associated wavelengthdependent PSF changes between different colors (or differentwavelengths) of the same or different viewing channels (e.g., leftand/or right eye viewing channels), and/or similar differences/changesin the same colors (different wavelengths) of different or same viewingchannels.

In various embodiments, the present invention may be a dual modulationprojector containing a pre modulator, relay optics, and a primarymodulator, and where pre-compensation for imperfections of the relayoptics PSF is made by modifying the image sent to the pre modulator. Thepre-compensation filter is different for different regions of the image.The precompensation filter coefficients may be calculated based upon PSFmeasurements and a reference desired PSF. Additional compensation ismade in the primary modulator. The pre-modulator image may be a halftoneimage on a DMD, and the primary modulator may be a DMD. The halftoneimage may be changed multiple times per frame, and where the bitsequences on the pre-modulator DMD and primary modulator DMD aresynchronized, such that the average across the frame is the product ofthe average of the pre-modulator images through the relay optics and theprimary modulator image.

The present invention may comprise a projector comprising apre-modulator to modulate light into a first image, a primary modulatorconfigured to further modulate the light to produce a desired image, andrelay optics configured to transfer the modulated light of the firstimage to the primary modulator, wherein the transfer optics are furtherconfigured to spread pixels of the first image so that each pixel of thefirst image illuminates a plurality of pixels of the primary modulator.The invention may further comprise a controller configured to energizethe first modulator with a backlight image based on image data of thedesired image, the backlight image further comprising an adjustment ofpixels of the backlight image to compensate for non-uniformity on theprimary modulator of one or more of the first image pixels. Thecompensation may comprise a difference between a desired point spreadfunction of light transferred from the pre-modulator to the primarymodulator and a PSF and/or MTF of the relay optics. The backlight (orpremodulator) image comprises a convolution of a low resolution versionof the desired image and the difference. The compensation may comprise acompensation scheme selected from a plurality of compensation schemesbased on the desired image. The compensation may comprise a non-linearequation adjusted based on the desired image. The compensation maycomprise a compensation scheme selected or derived based on a spatialfrequency parameter of the image and a wavelength of light beingmodulated. The compensation may comprise one or a combination of aplurality of compensation schemes applied to different portions of thebacklight image.

A projector according to the invention may comprise a multi-colorchannel projector each channel comprising a similar configuration of apre-modulator, primary modulator, and transfer optics, said controllerenergizing each pre-modulator with image data comprising a backlightimage for each color channel along with a color specific compensation.The compensation may comprise an inverse of a non-uniformity ofspreading of pixels of the pre-modulator onto multiple pixels of theprimary modulator according to wavelengths of light modulated in eachchannel. The first modulator may comprise one of a transmissivemodulator and a reflective modulator, and the primary modulatorcomprises one of a transmissive modulator and a reflective modulator,and the first modulator and second modulator are not necessarily thesame type of modulator.

Projectors according to the present invention may comprise modulators ofdifferent types or the pre-modulator and primary modulators are both DMDmodulators. The pre-modulator and primary modulators may beLiquid-Crystal-on-Silicon (LCoS) modulators. Any of the projectors maybe configured for projecting 3D images such as wherein the pre-modulatorimages comprise 1st and 2nd channel images of a 3D image, and thepremodulator may be energized by compensated pre-modulator imagescomprising left and right images of a 3D image, and wherein theprojector is part of a system for displaying an viewing 3D imagescomprising glasses comprising filters corresponding to the left andright images comprising filter passbands encompassing wavelengths of theleft and right images.

In the 3D embodiments, the wavelengths of the left image may originate,for example, from a laser light source illuminating a pre-modulatorwhile being energized with a compensated pre-modulator left imagecorresponding the illuminating wavelengths in a left image time frame;wavelengths of the right image originate from a laser light sourceilluminating the pre-modulator while being energized with a compensatedpre-modulator right image corresponding to the illuminating wavelengthsin a right image time frame.

The projectors of the present invention in multi-view and/or 3Dembodiments may be, for example, part of a system for displaying andviewing 3D images and the modulated desired images are passed viawavelength selective filters in 3D viewing glasses such that modulatedwavelengths of the left images of the 3D images are passed by a leftfilter of the 3D viewing glasses and modulated wavelengths of the rightimages of the 3D images are passed by a right filter of the 3D viewingglasses and the filters comprise passbands that are offset relative tothe wavelengths being viewed through the passbands such that wavelengthsof the compensated half-tone images further modulated into desired leftand right images by the primary modulator are passed via passbands thatencompass and are shifted toward longer wavelengths compared to thewavelengths of the intended image wavelengths passed through thepassbands. Such arrangement allow for capturing laser wavelengths partof compensated half-tone images further modulated for viewing at obliqueangles.

In describing preferred embodiments of the present invention illustratedin the drawings, specific terminology is employed for the sake ofclarity. However, the present invention is not intended to be limited tothe specific terminology so selected, and it is to be understood thateach specific element includes all technical equivalents which operatein a similar manner. Furthermore, the inventors recognize that newlydeveloped technologies not now known may also be substituted for thedescribed parts and still not depart from the scope of the presentinvention. All other described items, including, but not limited tomodulators, frames, sub-frames, etc. should also be considered in lightof any and all available equivalents.

Portions of the present invention may be conveniently implemented usinga conventional general purpose or a specialized digital computer ormicroprocessor programmed according to the teachings of the presentdisclosure, as will be apparent to those skilled in the computer art.

Appropriate software coding can readily be prepared by skilledprogrammers based on the teachings of the present disclosure, as will beapparent to those skilled in the software art. The invention may also beimplemented by the preparation of application specific integratedcircuits or by interconnecting an appropriate network of conventionalcomponent circuits, as will be readily apparent to those skilled in theart based on the present disclosure.

The present invention includes a computer program product which is astorage medium (media) having instructions stored thereon/in which canbe used to control, or cause, a computer to perform any of the processesof the present invention. The storage medium can include, but is notlimited to, any type of disk including floppy disks, mini disks (MD's),optical discs, DVD, CD-ROMS, CD or DVD RW+/−, micro-drive, andmagneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs, flashmemory devices (including flash cards, memory sticks), magnetic oroptical cards, SIM cards, MEMS, nanosystems (including molecular memoryICs), RAID devices, remote data storage/archive/warehousing, or any typeof media or device suitable for storing instructions and/or data.

Stored on any one of the computer readable medium (media), the presentinvention includes software for controlling both the hardware of thegeneral purpose/specialized computer or microprocessor, and for enablingthe computer or microprocessor to interact with a human user or othermechanism utilizing the results of the present invention. Such softwaremay include, but is not limited to, device drivers, operating systems,and user applications. Ultimately, such computer readable media furtherincludes software for performing the present invention, as describedabove.

Included in the programming (software) of the general/specializedcomputer or microprocessor are software modules for implementing theteachings of the present invention, including, but not limited to,preparing half-tone images corresponding to image data, dividing frames,synchronizing and applying bit sequences to DMDs, and the display,storage, or communication of results according to the processes of thepresent invention.

The present invention may suitably comprise, consist of, or consistessentially of, any of element (the various parts or features of theinvention and their equivalents as described herein. Further, thepresent invention illustratively disclosed herein may be practiced inthe absence of any element, whether or not specifically disclosedherein. Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed:
 1. A method for dual modulation display, comprising:applying a correction factor to uncorrected pre-modulator image data tobe sent to a pre-modulator to generate corrected pre-modulator imagedata; and energizing the pre-modulator with the corrected pre-modulatorimage data, the corrected pre-modulator image data including aconvolution of a low-resolution version of an image produced by aprimary modulator and the correction factor, wherein the primarymodulator receives light from the pre-modulator, wherein the correctedpre-modulator image data is a halftone image changed at least threetimes per frame of the pre-modulator, wherein energization signals usedto energize the primary modulator are changed at least one time perframe of the primary modulator, and wherein energizing the pre-modulatorwith the corrected pre-modulator image data is synchronized withenergization signals used to energize the primary modulator to providean average of the corrected pre-modulator image data and the imageproduced by the primary modulator.
 2. The method of claim 1, furthercomprising: illuminating the pre-modulator by a light source.
 3. Themethod of claim 1, wherein applying the correction factor furthercomprises applying the correction factor during the at least threehalftone images per frame of the pre-modulator.
 4. The method of claim3, wherein applying the correction factor during multiple halftones perframe of the pre-modulator is synchronized with a modified bit sequencein the primary modulator to produce a compensation image.
 5. The methodof claim 3, wherein applying the correction factor during multiplehalftones per frame of the pre-modulator further comprises applying thecorrection factor during a single frame period of a modulation period ofthe primary modulator and several sub-frame time periods of a modulationperiod of the pre-modulator.
 6. The method of claim 5, wherein pixelelements of the primary modulator are switched on/off once during thesingle frame period and pixel elements of the pre-modulator are switchedon/off once during a single sub-frame period and further that the singleframe period comprises a plurality of sub-frame time periods.
 7. Themethod of claim 1, wherein the corrected pre-modulator image dataincludes a left image and a right image of three-dimensional image.